CN109353043B - Polytetrafluoroethylene elastic band and preparation method thereof - Google Patents

Abstract

The invention relates to the elasticity of polytetrafluoroethyleneA polytetrafluoroethylene elastic band is prepared through thermal shaping at a temp higher than its smelting point, where the smelting point is lower than 330 deg.C and the density of elastic band is 0.5-1.0g/cm³The section of the elastic rubber is round, and the rebound rate is more than or equal to 20 percent; the preparation method of the polytetrafluoroethylene elastic band comprises the steps of refrigerating and screening polytetrafluoroethylene dispersion resin, mixing the screened polytetrafluoroethylene dispersion resin and a boosting agent on a mixing device, and performing curing treatment, preforming, pushing, degreasing treatment, stretching and heat setting treatment to obtain the polytetrafluoroethylene elastic band. The elastic polytetrafluoroethylene band has the rebound rate of over 20 percent, obviously improves the tensile strength and the compressive strength, is obviously superior to the existing elastic polytetrafluoroethylene band, has excellent creep relaxation resistance, chemical resistance and temperature resistance, can be used at the temperature of between 200 ℃ below zero and 260 ℃, and has simple preparation method and easy operation of process parameters.

Description

Polytetrafluoroethylene elastic band and preparation method thereof

Technical Field

The invention belongs to the technical field of preparation of sealing materials, and particularly relates to a polytetrafluoroethylene elastic band and a preparation method thereof.

Background

The polytetrafluoroethylene elasticity has good flexibility, compression resilience, creep resistance, high and low temperature resistance, and excellent corrosion resistance, non-aging property and self-lubricating property. Because of its excellent sealing performance and convenient installation and use, it is an indispensable sealing material in chemical, pharmaceutical, petrochemical, food and beverage, electronic, electric, metallurgical, marine and other industries.

The existing polytetrafluoroethylene elastic band in the market is basically not subjected to heat setting or is subjected to heat setting below the melting point, the rebound rate of the polytetrafluoroethylene elastic band is lower than 15 percent, the tensile strength is insufficient, and the requirement for sealing various sealing surfaces cannot be completely met.

Disclosure of Invention

Aiming at the defects of the existing polytetrafluoroethylene elastic band, the invention mainly aims to provide the polytetrafluoroethylene elastic band which has higher compression rebound rate and tensile strength, excellent creep resistance, better long-term sealing effect, longer service life and simple manufacturing process and the preparation method thereof on the premise of using pure polytetrafluoroethylene.

In order to achieve the purpose, the invention adopts the technical scheme that:

the polytetrafluoroethylene elastic band of the invention is subjected to heat setting at a temperature higher than the melting point, the melting point of a polytetrafluoroethylene elastic band product is below 330 ℃, and the density of the elastic band is 0.5-1.0g/cm³。

The cross section of the obtained polytetrafluoroethylene elastic belt is circular.

The rebound rate of the polytetrafluoroethylene elastic belt is more than or equal to 20 percent.

The preparation method of the polytetrafluoroethylene elastic band comprises the following steps:

1) refrigerating polytetrafluoroethylene dispersion resin, and then screening, wherein the refrigerating temperature is 0-19 ℃, the time is 24 hours, and the screening screen is 7-12 meshes;

2) placing the screened polytetrafluoroethylene dispersion resin and a boosting agent on mixing equipment for mixing, wherein the addition amount of the auxiliary agent is 16-22%, and standing;

3) curing at 5-50 ℃ for 5-48 hours;

4) preforming: pressing the cured mixture into a green body with the same shape as the cavity of the pushing and pressing machine;

5) putting the preformed blank into a die cavity of a pushing press for pushing to obtain a strip-shaped fiber bar;

6) degreasing the strip fiber bar, and controlling the temperature to be 150-250 ℃;

7) stretching: the temperature is controlled within the range of 50-330 ℃, the stretching force is controlled within the range, and the stretching magnification is 1.5-8 times;

8) heat setting: and (3) carrying out heat setting on the stretched strip at a high temperature, wherein the heat setting temperature is controlled to be 340-420 ℃.

The boosting agent in the step 2) is one of kerosene, solvent oil, petroleum ether or paraffin oil.

And 2) mixing the polytetrafluoroethylene dispersion resin and the boosting agent, putting the mixture on mixing equipment, rotating for 30 minutes, controlling the mixing temperature to be 0-19 ℃, and standing for 12-24 hours.

The preforming conditions in the step 4) are as follows: the pressure is 1.5MPa-3.0MPa, the compression speed is 10mm/min-50mm/min, and the pressure maintaining time is 10min-30 min; the diameter of the blank cavity is 1mm smaller than that of the pushing cavity.

In the step 5), the cone angle of the pushing mould for pushing is 25-35 degrees, the compression ratio is 40-120, the temperature of the pushing head is 40-60 ℃, and the extrusion speed is 30-150 m/min.

In the step 6), degreasing is to remove the boosting agent through three drying ovens with the temperature of 150-250 ℃.

The stretching in the step 7) is carried out on a stretching device, and the strip passes through a sintering furnace with a set temperature under the condition of a hot air heating mode, and different stretching ratios are realized by adjusting the final winding speed, wherein the stretching ratio is 1.5-8 times.

In the step 8), the heat setting is carried out by passing the stretched elastic belt through equipment in a hot air heating mode, wherein the traction speed is 0.5-5 m/min, and the temperature is controlled at 340-420 ℃;

the stretching process and the heat setting process of the polytetrafluoroethylene elastic belt are the most critical processes: polytetrafluoroethylene forms a node and fiber ultramicro structure by stretching, and the porosity and the micropore aperture size and uniformity before the fiber are adjusted by adjusting the stretching multiplying power, stretching tension and temperature, so that the physical and mechanical properties of the elastic belt are ensured; the temperature and time control of the heat setting will vary depending on the size of the polytetrafluoroethylene elastic tape, and generally, the higher the temperature used, the shorter the heating time, thereby producing a strong and resilient porous material.

The invention has the beneficial effects that: the elastic polytetrafluoroethylene band and the preparation method thereof have the advantages that the rebound rate of the elastic polytetrafluoroethylene band reaches more than 20 percent, the tensile strength and the compressive strength are also obviously improved, the elastic polytetrafluoroethylene band is obviously superior to the existing elastic polytetrafluoroethylene band, the creep relaxation resistance, the chemical resistance and the temperature resistance are excellent, and the elastic polytetrafluoroethylene band can be used at the temperature of-200 ℃ to +260 ℃.

Drawings

FIG. 1 is a process flow diagram of a method of preparing a polytetrafluoroethylene elastic tape;

FIG. 2 is a block diagram of a stretch-setting apparatus;

Detailed Description

The technical features of the present invention will be further described with reference to the following embodiments.

Example 1:

1) firstly refrigerating polytetrafluoroethylene dispersion resin, and then screening, wherein the refrigerating temperature is lower than 19 ℃, the time is 24 hours, and the screened screen is 10 meshes; the DF203 brand of the east Yue is selected as the resin;

2) mixing the screened polytetrafluoroethylene dispersion resin with a boosting agent, putting the mixture on mixing equipment, rotating for 30 minutes, and standing for 24 hours; the addition amount of the auxiliary agent is 19.5 percent; the auxiliary agent is preferably solvent oil Isopar M of Mobil;

3) curing at 35 deg.c for 20 hr;

4) preforming: pressing the mixture into a green body with the same shape as the cavity of the pushing machine; the pressure is 2.5MPa, the compression speed is 15mm/min, and the pressure maintaining time is 15 min; the diameter of the blank cavity is 1mm smaller than that of the pushing cavity;

5) putting the preformed blank into a die cavity of a pushing press for pushing to obtain a strip-shaped fiber bar; the cone angle of the pushing mould for pushing is 30 degrees, the compression ratio is 100, the temperature of a pushing machine head is 50 ℃, and the extrusion speed is 90 m/min;

6) degreasing: the temperature is controlled to be 150-250 ℃; degreasing is to remove the boosting agent by three baking ovens with the temperature of 150 ℃, 200 ℃ and 250 ℃;

7) stretching, wherein the temperature is controlled at 250 ℃, the stretching force is controlled within a range, the introduction rate of the stretching is controlled at 1m/min, and the stretching magnification is 1.5 times;

8) heat setting: and (3) performing heat setting on the stretched strip material at a high temperature, and controlling the traction speed to be 0.8m/min and the temperature to be 380 ℃ by using equipment in a hot air heating mode.

Example 2:

the stretching magnification in the stretching step was 2.0 times, and the other conditions were the same as in example 1.

Example 3:

the stretching magnification in the stretching step was 2.5 times, and the other conditions were the same as in example 1.

Example 4:

the stretching magnification in the stretching step was 3.0 times, and the other conditions were the same as in example 1.

Example 5:

the stretching magnification in the stretching step was 4.0 times, and the other conditions were the same as in example 1.

Comparative example 1:

the stretching ratio in the stretching step was 2.5 times, the heat-setting temperature was 280 ℃, and the other conditions were the same as in example 1.

The measurement data of the polytetrafluoroethylene elastic tape of examples 1 to 5 and comparative example 1 are shown in the following table:

as can be seen from the data in the table, the rebound rate of the polytetrafluoroethylene elastic belt in the examples 1-5 is greatly improved compared with that in the comparative example 1, the tensile strength is also obviously improved, and the melting point of the polytetrafluoroethylene elastic belt is below 330 ℃ after heat setting.

Claims (2)

1. The preparation method of the polytetrafluoroethylene elastic belt is characterized by comprising the following steps:

1) firstly refrigerating polytetrafluoroethylene dispersion resin, and then screening;

2) placing the screened polytetrafluoroethylene dispersion resin and a boosting agent on mixing equipment for mixing and standing;

3) carrying out curing treatment;

4) preforming: pressing the cured mixture into a green body with the same shape as the cavity of the pushing and pressing machine;

5) putting the preformed blank into a die cavity of a pushing press for pushing to obtain a strip-shaped fiber bar;

6) degreasing the strip fiber bar;

7) stretching: the temperature is controlled within the range of 50-330 ℃, the stretching force is controlled within the range, and the stretching magnification is 1.5-8 times;

8) heat setting: the stretched elastic belt is passed through equipment in a hot air heating mode, the traction speed is 0.5-5 m/min, and the temperature is controlled at 340-420 ℃;

the prepared polytetrafluoroethylene elastic band is subjected to heat setting at a temperature higher than the melting point, the melting point of a polytetrafluoroethylene elastic band product is below 330 ℃, and the density of the elastic band is 0.5-1.0g/cm³；

The section of the obtained polytetrafluoroethylene elastic belt is circular;

the rebound rate of the polytetrafluoroethylene elastic belt is more than or equal to 20 percent.

2. The method for preparing polytetrafluoroethylene elastic band according to claim 1, wherein the boosting agent in step 2) is one of kerosene, solvent oil, petroleum ether or paraffin oil.

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